Aquafacts / Jellies


You've got questions about jellies and we've got answers! Her are some of the most frequently asked questions, answered by our biologists and other reputable sources.

Quick info

96% water

Jelly body composition

3% protein

Jelly body composition

1% minerals 

Jelly body composition


Noticeable jelly species

Australian box jelly 

World's most poisonous jellyfish

What are jellies?

Jellies belong to the phylum Cnidaria, which has three major classes: Hydrozoa, the primitive fern-like creatures, many of which produce small jellies; Scyphozoa, the large jellies or scyphomedusae and their polyps; and Anthozoa, the sea anemones. Although many of these animals produce a jelly as part of their life cycle, there are only about 200 species of large jellies that people are likely to notice - most of these are in the class Scyphozoa.

What type of jellies does the Aquarium have?

Jellies you might see at the Aquarium include moon jellies (Aurelia labiata), lion’s mane jellies (Cyanea capillata), fried egg jellies (Phacellophora camtschatica), water jellies (Aequorea spp), Japanese sea nettles (Chrysaora pacifica), Pacific sea nettles (Chrysaora fuscescens), spotted jellies (Mastigias papua) and red eye medusas (Polyorchis penicillatus). Moon jellies are the species most likely to be on exhibit all the time.

Where can you find jellies?

Jellies live in all the world's oceans.

How do they swim?

Jellies swim by jet propulsion. The jelly will expand then quickly contract its bell-shaped body, which forces water away from the bell and pushes the jelly in the opposite direction.

What does the Aquarium feed its jellies?

The jellies at the Aquarium are fed a daily meal of larval brine shrimp that have been enriched with fatty acids, as well as frozen copepods.

Can a jelly "repair" its damaged tentacles or other parts of its delicate body?

Yes, a jelly can regenerate small amounts of tissue that has been damaged.

Do jellies have eyes?

Jellies don't have eyes as we think of them, although some species have eyespots. Eyespots are light-sensitive spots on the rim of their bells called ocelli. Jellies also have sensory organs called rhopalia, which form a row of small round structures along the rim of the bell. The rhopalia include sensory organs called statocysts that help maintain the jelly's balance. When a jelly tips too far to one side, the statocyst will stimulate nerve endings that cause muscles to contract, turning the jelly right side up.

How do jellies sting?

Jellies have specialized stinging cells, called cniodocytes. Each of these cells contains a nematocyst which acts like a mini-harpoon. When a jelly touches something the nematocyst is released and injects toxin into the prey.


Monterey Bay Aquarium. Jellies: Online Field Guide. Wroebel, David and Claudia Mills. 1998. Pacific Coast Pelagic Invertebrates. Monterey Bay, CA: Sea Challengers.

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